[Bug 1481388] Re: NTP : Use-after-free in routing socket code after dropping root

[Eric Desrochers]

debdiff for precise


** Description changed:

+ [Impact]
+ 
+  * User experienced repeated segfaults at the same instruction pointer
+ 
+ i/o error on routing socket No buffer space available - disabling
+ segfault at 31 ip 0000000000000031 sp 00007ffff9f11788 error 14 in libpthread-2.15.so[7f967a5d9000+18000] 
+ 
+ The remove_ and delete_ functions remove the current element from the
+ asyncio_reader_list, and free it, respectively.
+ 
+ We then return back to the loop at the top, wherein the asyncio_reader variable still points at the now-freed element, whose contents are (in theory) now scrambled
+ by having link pointers, etc, from internal malloc state overlaying the data.
+ 
+ [Test Case]
+ 
+ You can easily reproduce the bug by :
+ 
+ - Lowering the sysctl value net.core.rmem_max
+ 
+ $ sysctl -w net.core.wmem_max=<LOWER_VALUE>
+ This sets the max OS send buffer size for all types of connections.
+ 
+ - Adding multiple network interfaces and static routes.
+ 
+ [Regression Potential]
+ 
+ None expected since the fix is already available upstream
+ (https://github.com/ntp-project/ntp.git) and Debian package.
+ 
+ If after installing the patch, user are receiving this kind of message in /var/log/syslog : "routing socket reports: No buffer space available".
+ The next step, would be to increase the "net.core.rmem_max" and "net.core.wmem_max" values equally until the "routing socket reports: No buffer space available" message no longer showed up.
+ 
+ [Other Info]
+ 
+ NTP upstream (https://github.com/ntp-project/ntp.git)
+ [Bug 2224] Use-after-free in routing socket code after dropping root. - Commit: d6df9d3
+ [Bug 2890] Ignore ENOBUFS on routing netlink socket. - Commit: db47bd4 
+ 
+ The use-after-free bug has been fix in Debian release (closes: #795315)
+ Will submit the ignore-ENOBUFS-on-routing-netlink-socket in Debian in the next days.
+ 
+ [Original Description]
+ 
  We have 1 server (among hundreds) that its ntp service is crashing.
  
  A few minute/seconds after a start attempts we can see the following in syslog:
  ntpd[2729]: peers refreshed
  ntpd[2729]: Listening on routing socket on fd #49 for interface updates
  ntpd[2729]: i/o error on routing socket No buffer space available - disabling
  kernel: [157516.495224] ntpd[2729]: segfault at 31 ip 0000000000000031 sp 00007ffff9f11788 error 14 in libpthread-2.15.so[7f967a5d9000+18000]
  
  OS: Ubuntu 12.04.4 LTS
  Kernel: 3.11.0-19-generic
  
  I tried to compare it to other servers, and the only thing I could find that is different is that while it's up (before it crashes) I can see the following when running "lsof | grep ntp":
  ntpd 2729 ntp 49u sock 0,7 0t0 2473952565 can't identify protocol.

** Tags added: verification-done

** Changed in: ntp (Ubuntu Precise)
       Status: Confirmed => In Progress

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Title:
  NTP : Use-after-free in routing socket code after dropping root

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